1. Field of the Invention
The present invention relates to methods for sensing temperature and, more particularly, to a method for sensing temperature wherein a laser diode is used as a sensing element.
2. Description of the Prior Art
The sensing of temperature is a function that is required in a variety of arts. For example, the temperature of a material may need to be sensed so as to control its thermal distortion, or the temperature of an environment may need to be sensed so as to ensure an efficient operation of a resident system.
It is often required that temperature be sensed at a number of locations within an environment that contains a particular resident system. Such is true in an environment where there are large thermal gradients or where small variations in temperature can result in large system effects. For example, a typical space based optics system operates in an environment where there can be large thermal gradients depending upon the position of this system with respect to incident solar radiation, and where small variations in the temperature can result in large distortions of optical images.
Environments, or systems, that require temperature to be sensed at a number of locations generally use thermistors or thermocouples to accomplish the task. Although these types of temperature sensors are relatively simple and inexpensive, both require at least two electrical wires to be run from each temperature sensor to a temperature recording device. Thus, in a system such as a typical space optics system where as many as a hundred points are monitored for temperature, large and heavy cables comprised of several hundred electrical wires must be run between the sensed locations and the temperature recording device. Furthermore, due to a large amount of electromagnetic interference (EMI) in a typical space environment, the signals generated by the temperature sensors must be passed through expensive EMI filters. These large and heavy cables and expensive EMI filters are a burden when trying to design a low weight and low cost system.
Also, in many situations a rotating system requires temperature sensing. In these types of systems a thermistor is usually used in conjunction with a slip ring so as to maintain a continuous electrical connection between the temperature sensor and the temperature recording device. However, slip rings have only a limited life and they add considerable weight to a system. Thus, the use of a thermistor with a slip ring in a rotating system is another shortcoming that is associated with electrical temperature sensors. It is therefore desirable to overcome the above-mentioned shortcomings while providing an accurate and reliable temperature sensing scheme.